Research On Soil Fate Of Herbicides In Maize Field

Herbicides plays an important role in modern agriculture. The extensive application of herbicides in corn, which causes residual in soil, is an important factor affecting soil quality in agricultural production. Atrazine, nicosulfuron and mesotrione are applicated excessively in maize planting, causing environmental pollution of soil. As mesotrione is used with large quantities in the corn fields in recent years, studies on analysis and fate of mesotrione in soil has important theoretical value.With the attention to the herbicide residual contamination problems, a large number of research of herbicide biodegradation were done, which determines the microorganisms plays an important role in degradation of the herbicide in the soil and water. A group of microorganisms which can degrade or transform some herbicides were isolated. The main modes of action and pathway of microbial degradation of the herbicide have been defined. Therefore, the studies on fate of herbicide in the maize field soil has the vital significance to the application of herbicide.Through the instrumental analysis method, the microbial degradation of post-emergence herbicides in the corn fields is studied systematically, especially the fate and degradation characteristics of mesotrione in soil. The main results are as follows:(1) Aspergillus niger can degrade atrazine, nicosulfuron and mesotrione better.(2) The different inoculation amount of Aspergillus niger has different effects on the degradation of atrazine, nicosulfuron and mesotrione. With the different inoculation amount of Aspergillus niger, the degradation rate of the three herbicides is different. The degradation rate of the three herbicides is the fastest when the inoculation amount is 5%: the degradation rate of atrazine reaches 82.5%, the degradation rate of nicosulfuron reaches 93.8%, the degradation rate of mesotrione reaches 91.7%.(3) Optimum culture conditions of Aspergillus niger are as follows:p H 7, the concentration of mesotrione 10mg/L. Under the optimum conditions, the degradation rate of the Aspergillus niger is close to 100% within 72 h.(4) With the increasing of soil organic matter content, soil temperature and soil water content,degradation rate of mesotrione also increases. The optimum soil conditions of mesotrione degraded by Aspergillus niger in the soil are as follows: soil temperature 35 ℃, soil moisture content 40%and soil organic matter content 5.8%.(5) Different soil conditions effects on the leaching of mesotrione. With the increasing of mesotrione concentration and rainfall, the leaching depth of mesotrione in soil increases. With the increase of organic matter content in the soil, the leaching depth of mesotrione in soil decreases.Different soil types and the application of different additives make the leaching depth of mesotrione in soil different. The leaching depth of the black soil and the addition of 1% is the deepest, and the leaching depth of the meadow soil and the addition of 2% methyl esters is the lowest.(6) Different soil conditions effects on the adsorption of mesotrione. With the increasing of soil temperature and pH value, the soil adsorption capacity of mesotrione decreases. The higher the content of organic matter in the soil, the greater the adsorption of the soil to the mesotrione.Adding different additives make the soil adsorption capacity of mesotrione increases. The highest adsorption capacity is the addition of 2% methyl ester.